1. Field of the Invention
The invention relates to a molding apparatus for toric contact lenses. More particularly, the invention relates a molding apparatus for correcting angle of astigmatism with the toric contact lenses.
2. Description of the Prior Art
Astigmatism, a symptom of refractive abnormalities of the eye, refers to the phenomenon of imperfection image and incorrect place of focusing, where the refractive error creates superposed off-focus images, and in turn results in blurry and ghosted vision.
In general, there are two types of astigmatism: regular astigmatism and irregular astigmatism. A natural corneal surface should have a uniform curvature radius across its surface, spherically shaped like a basketball, whereas the astigmatism corneal shaped more like a rugby ball, differing in curvature between a steeper and a flatter meridians, has degree of astigmatism comparable to the difference in curvature radius of the two meridians. In the regular astigmatism, these two meridians generally have a constant curvature and are generally perpendicular to each other. Irregular astigmatism means the cornea may have more than two meridians of focus and they may not be 90° apart—in other words, the cornea has many irregularly shaped meridians at different angles.
In a normal eye, the cornea has a smooth surface and curvature, and its round surface is just like a basketball. Whereas, a person with astigmatism, has an oblong corneal surface shaped more like a rugby ball from end to end, rather than a round, spherical basketball. When light passes through an eye, the improperly shaped cornea bends different light rays at different meridians, which results in distorted and blurred vision. Cylindrical lenses are used to compensate for regular astigmatism.
A process flow for the production of toric contact lenses: providing a molding apparatus, a plastic mold is formed by injection molding through the use of the molding apparatus, casting a liquid monomer in the cavity of the plastic mold, polymerizing the monomer to form a solid, removing the lens from the cavity, and other processing steps, for example, hydration and extraction, may also be employed.
The molding apparatus comprises a convex inserter, a concave inserter, a convex inserter carrier, and a concave inserter carrier, wherein the convex inserter and convex inserter carrier are used for making a convex outer surface of toric contact lens, and the curvature in the head of the convex inserter shapes the curvature of the convex outer surface of the toric contact lens, and decides angle of astigmatism. The architectures of the convex inserter and convex inserter carrier are well known in the art, as discussed in U.S. Pat. No. 5,330,203.
However, in U.S. Pat. No. 5,330,203, the convex inserter and convex inserter carrier lack of labeling degree to an adjustment of angle of astigmatism, it is then impossible to adjust angle of astigmatism for toric contact lens directly through manipulating the inserter and the carrier; moreover, since the inserter and the carrier are deficient in positioning marks to each other, there is an absence of intense precision in adjusting astigmatism for the toric lens. Therefore, in the process of making toric lenses, without build-in positioning marks, it will be complicated to integrate precision calibration of astigmatism into the mold of machinery where the inserter and the carrier are installed.
The present invention offers a molding apparatus for toric contact lenses, capable of precisely and easily adjusting angle of astigmatism and its degrees, and relatively easy to assemble the inserter and the carrier in the mold of machinery while in the process of making lenses.